1. Field of the Invention
This invention relates to apparatus for treating horizontal structure surfaces, and more particularly, to a mobile surface abrading apparatus which utilizes air circulation to recycle rebounding abrasive from the surface through a separation system and into a hopper, where it is fed to an abrasive propulsion device, or devices, and where the abrasive media or particles are projected at the surface at high velocity in angular relationship and the rebounding abrasive particles and surface materials such as dust and debris, are recovered from the surface by air flow through one or more vertical abrasive conveyors. The mobile surface abrading apparatus is capable of operating with one or more mechanical conveyance devices providing energy to the abrasive particles for transporting the abrasive particles and surface debris to the separation system.
This invention is characterized by a continuous air flow system and an improvement in the lifting of abrasive and debris in a vertical or near-vertical direction with air movement alone, allowing two or more propulsion devices to treat the area adjacent to the air flow conveyor. The principle involves a selected air flow which is forced through restricted passages where particulate transfer is effected and non-restricted areas where separation of air and abrasive particles is accomplished. The abrading apparatus includes passages that allow abrasive and other particulate to be received from one or more angles, which facilitates an internal area of sufficient size to sustain an appropriate air velocity which forces the various particles to be encountered, both transversely in the sweeping function and upwardly in the conveying function, against the pull of gravity.
In the vertical conveying function, the maximum speed at which any object will fall is reached when atmospheric friction equals gravitational pull and this speed is known as the terminal velocity. The air flow system of this invention is designed to slightly exceed this terminal velocity and thus convey the abrasive particles upwardly through the apparatus. The pneumatic conveyance of abrasive particles in the apparatus of this invention would not normally require dust-handing equipment. Nonethless, the abrading operation is very dusty unless a dust collector is used and dust collection is mandated by environmental laws and common sense. Accordingly, a blower must be used to exhaust the cleaned air from the dust collector. This invention combines a dual purpose pressure blower that is properly sized for the volume and intensity necessary to satisfy the needs of the dust filters and the vertical abrasive and debris conveying chamber to recycle the spent abrasive particles.
Sweeping of the horizontal structure surface to be treated is accomplished by allowing air that usually leaks around surface seals to enter the blast area, normally from the trailing wall of the apparatus, in such a way that the abrasive particles do not escape. There is a constant spatter of abrasive particles at the point where the blast stream of abrasive particles strikes and deflects from the structure surface. An abrasive particle collision on or about the surface level at a sharp angle can cause the abrasive particles to project forcefully and abruptly in different directions. If an opening is located in the apparatus where abrasive particles can project, by deflection or directly, to the outside, these misdirected abrasive particles will escape at high speed, causing damage to machinery and constituting a danger to personnel in the immediate area. The apparatus of this invention facilitates entry of air at the trailing wall of the blast head, after being forced at high speed across a given structure surface area, without the danger presented by escaping particulate. Upon entry into the apparatus, air velocity sweeps through the machine and a small percentage of abrasive particles becomes wedged in the crevices where the blast head contacts the treated surface.
The improvement of this invention includes carefully forming a corridor in which the lower containment structure constitutes the treated structure surface area behind the blasting area and an upper wall that is adjustable in order to vary the internal air intake area, and therefore the velocity, of the upwardly deflected abrasive particles at a selected air flow. A pair of spaced floating and deflector seals contact and seal at the structure surface. A third side or wall is supplied with fixed resilient seal and a fourth, or trailing wall is open to the atmosphere for the intake of air. This corridor defines a passageway in which air is forced, either longitudinally or transversely, but in either case horizontally, across the structure surface immediately behind the blast travel area, in order to entrain loose abrasive and debris particles. This horizontal air flow has adequate force at structure surface level to entrain any loose particles lying there and convey the abrasive and debris particles through a labyrinth-type passageway. This passageway is constructed in such a way as t make it virtually impossible for any of the particles to escape the blast area under the force of retained kinetic energy.